The use of secondary batteries such as lithium-ion batteries has become widespread in recent years into such fields as electrically-powered equipment and storage of electricity. Demand for a number of batteries connected in series is increasing in order to address the issue of high voltage. At the same time, there is a great demand for securing long-term reliability and safety and improving battery longevity. When a battery back is formed by connecting a plurality of single batteries in series, it is ideally desirable in terms of reliability, safety and longevity that the voltages through the constituent batteries remain uniform in charge and discharge operations and in storage operation and the constituent batteries deteriorate in performance at the same rate until the life of all the constituent batteries comes to an end. However, in reality, the constituent batteries vary in performance, deterioration speed and the like. Therefore, the balance of voltage can be lost. In order to address the problem, the following measure is taken as disclosed in Patent Document 1: the voltage of the constituent batteries is monitored in general to provide protection against troubles such as an overcharge during charging, control the voltage balance, and perform other processes. Normally, in order to form a secondary battery block by connecting a number of batteries in series, a secondary battery is divided into unit blocks for every several batteries and a battery adjustment section is provided for each. Furthermore, the information from the battery adjustment sections is transmitted to a control circuit to control a charge and discharge switch and the like in order to control the secondary battery pack.
Patent Document 1: JP-A-2002-152982